This invention relates to high power testing of microwave transistors (DUT) in nonlinear operation, where the signal form is distorted and harmonic signal components are generated and must be processed. When the transistor is driven in its nonlinear operation regime, the internal impedance at the output of power transistors is very low. An impedance tuner used to match the transistor must also match such impedance. Passive impedance tuners can reach maximum reflection factors tuner |Γtuner| of the order of 0.95, corresponding to impedances of 2.4Ω. The insertion loss between DUT and tuner reduces the available tuning range at the DUT reference plane and thus the capacity of the passive tuner to match the transistor. The only remedy to this limitation is using active systems, i.e. test systems whereby a signal coherent with the signal injected into the transistor, is injected independently into the DUT output terminal and creates a virtual load. This additional signal can be the only one injected, in which case we speak of “active” load pull, or is can be superimposed to signal reflected by a passive tuner, in which case we speak of “hybrid” load pull; obviously if only a passive tuner is present, we speak of “passive” load pull. In both active injection cases the objective is reaching and conjugate matching the internal impedance of the transistor; in general terms a standard requirement is a dynamic range reaching a reflection factor |Γ|=1 (corresponding to an internal impedance of 0Ω). The objective of this invention is an active tuner apparatus, combining a modified reverse signal injection mechanism within a tuner architecture allowing |Γ|=1. Harmonic signal components are processed (matched with proper loads) using passive harmonic (20, 23) tuners. The typical test system is shown in FIG. 1:
A four port vector receiver (24, VNA), injects signal (25) into the DUT (21) via a source tuner (23), which is wideband or harmonic and a bidirectional coupler (11). The outgoing signal travels through a second bidirectional coupler (10) and a load harmonic tuner (20) which is terminated with characteristic impedance Zo (19), typically 50Ω. The injected and reflected power waves <a> and <b> into and from the DUT are measured by the VNA (24), after being sampled by the couplers (10, 11). The tuners and instruments are controlled digitally (18, 17) by a system controller (22) running appropriate test software.